Feature
Understanding your options for hi-rel requires knowledge of component screening levels
the importance of availabilitymay outweigh the small cost penalty.
3. Are non-RoHS products still available?
Yes. This is primarily due to the tin whiskering phenomenon sometimes associated with lead-free parts. This can cause short circuits that are difficult to identify during visual inspection of the assembled printed circuit board.
Some manufacturers still offer, or have started
to offer again, non-RoHS parts with a tin/lead finish. International Rectifier, for example, has recently begun to offer a range of mosfets, IGBTs and drivers with a tin/lead (Sn/Pb) finish. These parts are designed to help manufacturers serving the aerospace industry by eliminating the tin whisker problem. Customers in this sector have previously been forced down the RoHS/lead-free route, which caused considerable manufacturing problems and sometimes resulted in parts having to be re-tinned at extra cost.
4. Can we specify lead finish on components?
Yes, on most discrete components, but there is a small additional cost. Some of the manufacturers that Solid State Supplies deals with will offer an option for devices to be solder dipped to give a finish with a defined minimum amount of lead. Some devices are offered with a 60/40 typical lead finish but others, such as discrete diodes, are normally 90/10 Sn/Pb.
Where customers need aminimumamount of lead that is
greater than this, we suggest that parts are solder dipped, so that they also have a 60/40 Sn/Pb final
finish.Many companies offer this dipping service, but to ensure effective quality control we have this carried out by the componentmanufacturer, so no third parties are involved.
5. Can low-cost plastic parts be used inmilitary applications?
Yes, there are a number ofmanufacturers now offering plastic parts that are screened in accordance withmilitary specifications. This is sometimes called upscreening. Itmeans
20 | April 2011
Solid State Supplies limits its number of suppliers, in order to enhance its technical support
the parts are put through the same screening flow as JAN, JANTX and JANTXV, but the parts are not present on any qualified products list (QPL).
One example of just such a
list is theMil-PRF-19500 list produced by the Defence Supply Centre Columbus (DSCC) in the United States, which lists manufacturers who make parts to approved standards.When parts are supplied as ‘tested in
accordance with’ a particular specification, there will usually be an ‘X’ in the part numbers for products screened to JANTX level and a ‘V’ in the part numbers for products screened to JANTXV level.
These parts usually come from test houses, but also from
manufacturers who cease manufacturing QPL components but still want to offer a suitable substitute to the market. The ‘X’ or ‘V’ could be in the prefix or suffix of a part number. For example,MX may indicate JANTX screening or SCV denote JANTXV screening. There are, of course, many other possible combinations. These components tend to be popularly specified parts that could also be suitable for high-reliability applications when screened.
And finally
So how can Solid State Supplies help? It supports UK electronic equipmentmanufacturers with products focused on twomain areas: embedded processing and connectivity and power semiconductors andmodules. In order to enhance its technical and commercial support, Solid State Supplies has chosen to represent a limited number of suppliers. These include global brands and niche companies that offer products with exceptional performance in specific applications includingmilitary and aerospace, industrial andmedical electronic equipment. A UK- based inventory supports fast, reliable delivery.
www.sssplc.com www.electronics-sourcing.co.uk
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